Several solutions have already been proposed for the energizing of a motor winding with energy just sufficient to assure stepping. For instance in the case as described in Swiss Pat. No. 585 428, whenever during the energizing period of the motor there has been detected a minimum current in the winding, it may be concluded that the rotor will step since this minimum current corresponds to the maximum speed of the rotor. It may however be shown that what has just been said is not always the case and such may be verified from the description and drawings which accompany the French patent application No. 2 459 579. This latter citation proposes to overcome the difficulties by the employment of means based on an integration of the mutual flux difference magnet-to-winding in order to detect whether the rotor has stepped or not. If this arrangement is very sure by virtue of the spread of amplitudes measured between a successful step and a missed step, it presents the difficulty of requiring an integrator provided with a capacitor, this being difficult to miniaturize beyond certain limits. Moreover, this arrangement detects only whether or not the step has been made but does not propose any solution to adapt the length of the motor pulse to the real load which is applied to the motor.
The purpose of this invention thus is to overcome the above cited difficulties and to provide a method for slaving the operation of a stepping motor to the load imposed on its rotor, this in accordance with the definitions in the claims.